1. Field of the Invention
The present invention relates to a liquid immersion optical tool, a method for cleaning the liquid immersion optical tool, a liquid immersion exposure method and a method for manufacturing a semiconductor device, wherein a liquid immersion medium fluid layer is provided between an optical lens system and an object, improving an optical performance.
2. Description of the Related Art
A liquid immersion microscope or a liquid immersion exposure tool and the like is used as a liquid immersion optical tool for immersing liquid immersion medium fluid between an object and an optical lens system, thereby improving a resolution and a depth of focus. In a liquid immersion microscope, a liquid immersion medium liquid such as oil or water is provided between an objective lens of the microscope and an object, thereby improving a resolution and a depth of focus. In a liquid immersion exposure tool for use in a semiconductor lithography process, a liquid immersion medium fluid is provided between a lens and a wafer, thereby making it possible to increase NA (Numerical Aperture) and to increase a depth of focus. This exposure tool is expected to be a main exposure tool in manufacturing a semiconductor device in a generation following a 65 nm half pitch generation (WO 99/49504).
The lens of the liquid immersion optical tool is in contact with liquid immersion medium fluid for a long time when the liquid immersion optical tool is used. Thus, there is a problem that substances generated from the tool, the object surface, and a structure for guiding the liquid immersion medium fluid react with each other to adhere to the lens so that the lens surface is clouded. This clouding of the lens surface is problematic because it degrades the resolution and the luminescence.
In addition, there is a problem that the substance or impurities adhered to the lens or members of the tool contaminate the object surface.
In addition, portions having been contacted with the liquid immersion medium fluid include a liquid immersion head, an object stage, and a liquid immersion medium fluid supply and discharge device. There is a problem that, when the liquid immersion optical tool is used for a long time, impurities adhere to their associated portions, and the adhered impurities reach an object and contaminate the object surface.
Furthermore, there is a problem that, when the liquid immersion medium fluid supplied between the lens and the wafer is not clean before and during exposure, the exposure cannot be properly carried out.